Highly flowable thermoplastic compositions are of interest for a wide variety of injection molding applications. By way of example, thin-walled components in the electrical, electronics and motor vehicle industry require low viscosities from the thermoplastics composition in order to permit material to be charged to the mold with minimum injection pressures and, respectively, clamping forces in the appropriate injection molding machines. This also applies to simultaneous charging of material to two or more injection molding components by way of a shared runner system in what are known as multicavity tooling systems. Shorter cycle times can moreover often be achieved using low-viscosity thermoplastic compositions. Good flowabilities are also specifically very important for highly filled thermoplastic compositions, e.g. with glassfibre and/or mineral contents above 40% by weight.
However, although the thermoplastic compositions have high flowability, the actual components produced therefrom are subjected to stringent mechanical requirements, and the lowering of viscosity cannot therefore be permitted to impair mechanical properties.
There are a number of ways of obtaining highly flowable, low-viscosity thermoplastic molding compositions.
One way uses low-viscosity polymer resins with very low molecular weight as base polymers for the thermoplastic molding compositions. However, the use of low-molecular-weight polymer resins is often associated with sacrifices in mechanical properties, in particular toughness. Preparation of a low-viscosity polymer resin in an existing polymerization plant moreover often requires complicated intervention attended by capital expenditure.
Another way uses what are known as flow aids, also termed flow agents or flow assistants or internal lubricants, which can be added as an additive to the polymer resin.
These flow aids are known from the literature, e.g. in Kunststoffe 2000, 90 (9), p. 116-118, and by way of example can be fatty acid esters of polyols, or amides derived from fatty acids and from amines. However, these fatty acid esters, such as pentaerythritol tetrastearate or ethylene glycol dimonitanoate, have only limited miscibility with polar thermoplastics, such as polyamides, polyalkylene terephthalates or polycarbonates. Their concentration increases at the surface of the molding and they are therefore also used as mold-release aids. Particularly at relatively high concentrations, they can also migrate out of these moldings to the surface on heat-ageing and become concentrated at the surface. By way of example, in coated moldings this can lead to problems with regard to adhesion to paint or to metal.
As an alternative to the surface-active flow aids, it is possible to use internal flow aids which are compatible with the polymer resins. Examples of those suitable for this purpose are low-molecular-weight compounds or branched, highly branched or dendritic polymers whose polarity is similar to that of the polymer resin. These highly branched or dendritic systems are known from the literature and their basis can by way of example be branched polyesters, polyamides, polyesteramides, polyethers or polyamines, as described in Kunststoffe 2001, 91 (10); pp. 179-190, or in Advances in Polymer Science 1999, 143 (Branched Polymers II), pp. 1-34.
EP 0 682 057 A1 describes the use of the nitrogen-containing first-generation 4-cascade dendrimer: 1,4-diaminobutane[4]propylamine (N,N′-tetrabis(3-aminopropyl)-1,4-butanediamine) DAB(PA)4 to lower viscosity in nylon-6, nylon-6,6 and polybutylene terephthalate. While use of DAB(PA)4 to lower viscosity in polyamides has practically no effect on the impact resistance of the resultant molding compositions (difference <5%), impact resistance falls by more than 15% in the case of PBT.
WO-A 98 27159 describes an improvement in toughness of glassfibre-reinforced polyesters or polycarbonates via use of two copolymers composed of ethene and of acrylates, one copolymer also bearing a reactive epoxy or oxirane function. Flow improvement in the molding compositions is an object of the invention, but the comparison system described composed of polyester and of the copolymer composed of ethene and methylacrylate has higher melt viscosity than the pure polyester system.
JP 01247454 describes mixtures which have low-temperature toughness, of polyesters with a copolymer composed of ethene and of an unreactive alkyl acrylate whose MFI is 5.8 g/10 min (at 190° C., 2.16 kg) and with a copolymer composed of ethene and of an acrylate having an additional reactive group. The subject of that application is not flow improvement in molding compositions.
EP-A 1 191 067 (=U.S. Pat. No. 6,759,480) describes the impact modification of thermoplastics, inter alia of polyamide and polybutylene terephthalate via a mixture composed of a copolymer composed of ethene with an unreactive alkyl acrylate, and also of a copolymer composed of ethene with an acrylate having an additional reactive group. There is no discussion of the flowability of the molding composition.
EP-A 0 838 501 (=U.S. Pat. No. 6,020,414) describes mixtures having low-temperature toughness of reinforcing materials and polyesters with a copolymer composed of ethene and of an unreactive alkyl acrylate, and also with a copolymer composed of ethene and of an acrylate having an additional reactive group. The best embodiment in that application is achieved with a copolymer composed of ethene and methyl acrylate. The subject of that application is not flow improvement in molding compositions.
WO-A 2 001 038 437 (AU 4 610 801 A) describes mixtures composed of polyester with a core-shell rubber and with two different copolymers composed of ethene and of acrylates with and without additional reactive groups. The toughness of the molding compositions can be improved, and the flowability even of the binary mixtures composed of polyester and of one of the other constituents mentioned is, according to Table 4 and Table 9, not better for the mixtures used than for the pure polyesters. The copolymer used composed of ethene and 2-ethylhexyl acrylate has an MFI value (MFI=Melt Flow Index) of 2 g/10 min (at 190° C., 2.16 kg).
FR-A 28 19 821 describes the use of copolymers composed of ethene with 2-ethylhexyl acrylate whose MFI is smaller than 100 as a constituent of hot-melt adhesive mixtures. There are no indications of applications for elastomer modification or flow improvement of semicrystalline thermoplastics.